Method of manufacturing a klystron



May 26, 1964 F. L. sALlsBuRY METHOD oF MANUFACTURING A KLYsTRoN Original Filed March 25, 1954 ul .1A m-H A w m lm-HMHMA ,.N .AMI MII. wm a m wmf A am W Mm `N` E NNI. I Q mw -N\ M A A m n Q nu .Q .QN R Q Q E ww ..41 uw N A v M um .NWN A/LI |r| @n ww N Q JH lm-HIMH .Www NN r f A x w M J/ mm m I R um N A v3 A hv Q A A Nm h.. i f m my. En mm l .I1 wwf. om .hf WW vv wv n n .1 1| NQ -L. NV s 0N MAI- United States Patent Oce 3,134,160 Patented May 26, 1964 3,134,160 METHOD F MANUFACTURING A KLYSTRON Frederick l... Salisbury, Los Altos, Calif., assigner to Varian Associates, San Carlos, Calif., a corporation of California Application May 14, 1959, Ser. No. 813,157, now Patent No. 3,047,351, dated July 31, 1962, which is a division of application Ser. No. 418,714, Mar. 25, 1954, now Patent No. 2,892,121, dated June 23, 1959. Divided and this application Nov. 29, 1961, Ser. No. 155,750

3 Claims. (Cl. 29-25.11)

This invention relates to electron discharge devices and, more particularly, to an electron discharge device of the velocity modulation type arranged to operate at microwave frequencies.

As the operating frequency of electron discharge devices or tubes has increased, a corresponding increase has been noted with respect to the critical nature of the alignment of the elements thereof, the Igeometric shape and tolerances of such elements, and the losses of energy resulting from any deviation in these 4tube design factors. While the design problems presented have been severe with tubes such as reflex klystrons and two-cavity klystron amplifiers, they have been further accentuated, for obvious reasons, with multi-cavity klystrons, particularly when frequencies of the order of 20-30 kmc. are approached. In such cases, since a wavelength is in the neighborhood of one centimeter, even such minor structural aberrations as produced by brazing can affect the losses and the tunability of the amplifier.

Accordingly, a feature of the present invention involves the provision of a velocity modulation tube of relatively simple construction.

A further feature is the provision of `a microwave tube of the multi-cavity type having a structural arrangement which facilitates assembly and efficient operation thereof.

Yet another feature of the invention is the provision of a microwave tube structurally arranged to insure proper alignment of the parts and the maintenance of design tolerances.

These and other features will become more apparent from the following description of a preferred embodiment of the present invention as shown in the accompanying drawing wherein:

FIG. l is an elevational view of a multi-cavity microwave amplifier, parts being cutaway to illustrate features of construction.

FIG. 2 is a section taken along line 2-2 of FIG. l, and

FIG. 3 is an enlarged view partially in section illustrating interior construction of the resonator cavities of the amplifier.

The microwave amplifier generally includes a beamproducing section l followed by la central section 11 wherein the interaction between the beam and the applied radio frequency wave takes place to provide the amplification and `a collector section 12 where the electrons of the spent beam are collected.

In `accordance with the invention, the amplification section 11 of the tube preferably has a body formed from -a substantially semi-cylindrical block 13 of copper, as best illustrated in FIG. 2. A cylindrical bore 14 which extends longitudinally through the semi-cylindrical block 13 is intersected by a number of spaced transverse bores 15 extending from the flattened side 21 of the block 13 and is adapted to receive la plurality of drift tube members 17. Each member 17 comprises a copper cylinder which is provided with -small cylindrical extensions 1S at its ends and bas a central bore extending therethrough and through such extensions to provide a drift space 19 for the electron beam. When the members -17 tare inserted in the bore 1.4 in properly spaced relation, as determined by Ithe spacing of the transverse bores 15, resonator cavities 16 of the desired frequency are formed between adjacent members. Prior to insertion of the copper drift tube members 17 into the bore 14, the latter is provided by a flash-plating technique with la thin layer of silver. "Ibe exterior dimension of the drift tube members 17 is slightly greater than the diameter of the plated bore l-14 through the ldescribed semi-cylindrical block 13 so that upon insertion a pressed-fit is obtained. .After the insertion of the drift tube members 17, a single heating operation will cause the copper and silver -to alloy and the members to be fused vwithin the bore. It should be noted that the same fusing technique and resulting assembly `can be employed with drift tube members 17 which are not of solid copper construction; for example, copper- IClad molybdenum drift tube members can be utilized in the fabrication. This technique obviously avoids the mentioned difficulty of conventional brazing methods, and a clean juncture is formed between the drift tube members 17 and the bore 14 which provide, in effect, the Walls of the resonator cavities `16.

An inner drift tube member 17 which is machined to provide the theoretically desired geometry to as close tolerances as possible is first inserted and, in turn, each of the adjacent drift tube members 17 is inserted to an extent slightly less than that required to provide the spacing productive of the desired resonant frequency of the cavities 16. Subsequently, radio frequency energy is supplied to each cavity 16 between adjacent drift tube Imembers through the respective one of the transverse bores 15 extending from the flattened side 21 of the semi-cylindrical block 13. While radio frequency energy of the desired frequency is inserted through the transverse bore 15 a slight axial movement is imparted to the drift tube member 17 until the resonance condition is achieved, this then being the final disposition of the member. The above-described technique has been found not only desirable but actually indispensable to produce the desired cavity dimensions when operating at frequencies between 20 and 30 kmc. because lat such frequencies normal machining operations have insufficient accuracy to effect the desired structural tolerances.

As is shown clearly in FIG. 3, the first and last cavities 16 of the illustrated five-cavity amplifier are completed by members 17', which in effect constitute one-half of the complete drift tube members 17 previously described, in the intermediate portions of the bore 14.

To provide coupling of radio frequency energy into and out of the amplifier, the described semi-cylindrical block 13 is cut away in its lower portion forl the reception of conventional waveguide sections 22 which communicate with the first and last resonator cavities 16 through bored iris openings 23. A mica Window 24 is suitably secured at the end of each of the waveguide sections 22 to maintain the vacuum within the cavities 16 and the remainder of the tube.

The previously mentioned bores 15 are enlarged adjacent the flattened side 21 of the semi-cylindrical block 13 as indicated at 20 to receive in vacuum-tight relation a tuning diaphragm 25 secured at the end of a tuning screw 26 which is adjustably suspended from the lateral arm 27a of a bracket 27 secured to the flattened side 21 of the block 13 by suitable screws 28. The diaphragms 25 are maintained in adjusted position by pairs of lock nuts 29, 30 on the tuning screws 26, which nuts engage respectively the upper and lower surfaces of the lateral bracket arm 27 a.

The beam-producing section 10 includes a substantially cylindrical hollow body 31 having a cathode button 32 and associated heater element 33 and focusing ring 34 mounted centrally therein and axially aligned with a. tapered bore 35 formed in the base of an attached pole piece 36 of magnetic material and adapted to register with the aligned 9 E drift spaces 19 in the drift tube members 17, 17' within the amplification section 11 of the tube. T o assure that such alignment is achieved, the cathode button 32 is provided with a small central aperture 32a which enables the cathode 32 and the drift tube members 17, 17' of the tube to be aligned optically; that is, a light may be positioned at the end of the beam-producing section and the same laterally shifted until such light passes through the small central aperture 32a in the cathode button 32, the registering bore 35 in the pole piece 36 and the drift tube members 17, 17 so as to be visible to a viewer Whose eye is adjacent the drift space 19 at the output end of the amplification section 11. While so aligned, the beamproducing section 10, or more particularly, the attached pole piece 36 is annularly brazed or otherwise secured to the amplification section 11 of the tube so that the alignment will be maintained.

The collector section 12 of the electron discharge device is preferably mounted on the second cup-shaped pole piece 38 having a tapered bore 39 extending centrally through its base and adapted to register with the aligned drift spaces 19 when said cup-shaped element is brazed in position at the output end of the amplification section 11 of the tube so as to accommodate the electron beam. Such alignment is again attained by the optical technique described above. The collector section 12 includes an elongated member 40 having a deep cylindrical recess 41 machined therein and arranged so that its open end is adjacent and axial with the tapered bore 39 in the pole piece 38. The tWo elements are secured in such relation through a glass-to-metal seal 42 formed between tubular stubs 43, 44 extending in opposite directions from an annular cap 45 on the cup-shaped pole piece 38 and a thick sleeve 46 telescoped onto the outer end of the elongated collector member 40. This construction and insulated mounting of the collector enables current readings to be taken when desired.

Tubulations 47 in the side of the two pole pieces 36, 38 enable evacuation of the tube after completion of the assembly, and are then pinched off as shown in FIG. 1. To facilitate evacuation, eccentric axially-extending passages 48 are formed in the drift tube members since the actual diameter of the drift spaces 19 will be somewhat less than .02 at the mentioned operating frequencies. Because these passages 48 are relatively Well below cutoff at the operating frequency, no radio frequency energy can be transmitted therethrough.

The tube is electrically connected quite conventionally, a battery 50 being arranged, as shown in FIG. l, to provide heater current, and a second battery 51 to provide positive D.C. voltage for the central and collector sections 11, 12 of the tube. Conventional coils, indicated at 52, 53, are disposed adjacent the pole pieces 36, 38 to provide for proper focusing of the beam during its traverse through the tube. In operation, thebeam of electrons emitted from the cathode button 32 is accelerated through the bore 35 and into the small cylindrical bores through the drift tube members 17. The radio frequency signal'to be amplified is fed into the first or buncher cavity resonator through the input waveguide 22. The radio frequency electric field produced across the resonator gap in this first cavity resonator velocity modulates the electrons, that is, the electrons are slowed down or speeded up depending on the phase of the radio frequency field across the gap at the time of transit of the electron. In the fieldfree drift space defined by the first drift tube member 17 and extensions 18, the velocity modulation forms the beam into groups or bunches of electrons which, at their point of sharpest bunching, pass through the resonator gap in the second cavity resonator. All of the cavity resonators are so proportioned as to size and gap spacing as to be sharply resonant at the desired operating frequency of this cascade amplifier. The cavity resonators are initially tuned during assembly by the proper positioning and brazing of the drift tube members 17 to establish correct resonator gap spacing, the cavities thereafter being tine-tuned by means of the diaphragms 25. All of the cavity resonators between the first or input resonator and the last or output resonator serve to improve the bunching of the electron beam initiated in the first cavity resonator so that optimum bunching is produced before the beam passes through the resonator gap in the last or output resonator. The amplified radio frequency energy is passed out from this cascade amplifier through the output waveguide 22. An actual tube which has been constructed and operated with 1500 volts on the sections 11, 12 has produced a gain of as high as 74 decibels, as a result of the minimization of losses through the described arrangement in accordance with the invention. What losses do occur, of course, appear as heat in the amplification and collector sections 11, 12 of the tube and are easily dissipated because of the large volume of the semicylindrical block 13 and the thick sleeve 46 on the collector member 48, no cooling ns being required.

The present application is a division of United States patent application Serial No. 413,157 tiled May 14, 1959, now Patent No. 3,047,351, which in turn is a division of United States patent application Serial No. 418,714 filed March 25, 1954, now U. S. Patent 2,892,121.

Since many modifications and variations in the described arrangement can obviously be made without departing from the scope of the invention, it is intended that all matter in the foregoing description or shown in the drawing shall be interpreted as illustrative and not in a limiting manner.

What is claimed is:

1. In the method of manufacturing a klystron including a metallic body and having a plurality of drift tube members forming the end walls of a plurality of cavity resonators in the longitudinal bore through said metallic body, the surfaces of the bore in the body forming the side walls of the cavity resonators, the method of securing the drift tube members in the bore so as to form a plurality of successive cavity resonators having desired resonant frequencies which comprises the steps of plating the surface of the bore with a high electrically-conducting material, inserting the drift tube members within the bore in a force fit to their desired approximate spaced positions so as to form the plurality of cavity resonator chambers within the bore of the metallic body, supplying radio frequency into each of said cavity resonator chambers at the desired operating resonant frequency, adjusting the spacing of each of said drift tube members until the desired resonance condition is accomplished in each of the cavity resonators, and heating the metallic body and drift tube members to the temperature necessary to soften the plating material, the subsequent cooling of the body and drift tube members causing said drift tube members to be fused in the plated surface of the bore.

2. The method as claimed in claim l wherein said plating material is silver.

3. The method as claimed in claim 1 wherein the outer diameter of the drift tube members is slightly larger than the inner diameter of the bore after the plating has been placed thereon such that the drift tube members are initially inserted within said bore in a force iit into the Soft plating material.

References Cited in the iile of this patent UNITED STATES PATENTS 2,641,731 Lines June 9, 1953 2,708,249 Pryslak May 10, 1955 2,882,587 Unger et al. Apr, 21, 1959 

1. IN THE METHOD OF MANUFACTURING A KLYSTRON INCLUDING A METALLIC BODY AND HAVING A PLURALITY OF DRIFT TUBE MEMBERS FORMING THE END WALLS OF A PLURALITY OF CAVITY RESONATORS IN THE LONGITUDINAL BORE THROUGH SAID METALLIC BODY, THE SURFACES OF THE BORE IN THE BODY FORMING THE SIDE WALLS OF THE CAVITY RESONATORS, THE METHOD OF SECURING THE DRIFT TUBE MEMBERS IN THE BORE SO AS TO FORM A PLURALITY OF SUCCESSIVE CAVITY RESONATORS HAVING DESIRED RESONANT FREQUENCIES WHICH COMPRISES THE STEPS OF PLATING THE SURFACE OF THE BORE WITH A HIGH ELECTRICALLY-CONDUCTING MATERIAL, INSERTING THE DRIFT TUBE MEMBERS WITHIN THE BORE IN A FORCE FIT TO THEIR DESIRED APPROXIMATE SPACED POSITIONS SO AS TO FORM THE PLURALITY OF CAVITY RESONATOR CHAMBERS WITHIN THE BORE OF THE METALLIC BODY, SUPPLYING RADIO FREQUENCY INTO EACH OF SAID CAVITY RESONATOR CHAMBERS AT THE DESIRED OPERATING RESONANT FREQUENCY, ADJUSTING THE SPACING OF EACH OF SAID DRIFT TUBE MEMBERS UNTIL THE DESIRED RESONANCE CONDITION IS ACCOMPLISHED IN EACH OF THE CAVITY RESONATORS, AND HEATING THE METALLIC BODY AND DRIFT TUBE MEMBERS TO THE TEMPERATURE NECESSARY TO SOFTEN THE PLATING MATERIAL, THE SUBSEQUENT COOLING OF THE BODY AND DRIFT TUBE MEMBERS CAUSING SAID DRIFT TUBE MEMBERS TO BE FUSED IN THE PLATED SURFACE OF THE BORE. 